High availability multi-single-tenant services

A system comprising:

• data processing hardware;
• memory hardware in communication with the data processing hardware and storing instructions that, when executed on the data processing hardware, cause the data processing hardware to perform operations comprising:
• executing a pool of primary virtual machine (VM) instances, each primary VM instance executing a corresponding individual service instance;
• instantiating a shared secondary VM instance;
• identifying unavailability of a particular primary VM instance of the pool of primary VM instances;
• causing the corresponding individual service instance executing on the particular primary VM instance to failover to the share secondary VM instance to commence executing the corresponding individual service instance;
• and
• in response to the corresponding individual service instance failing over to the shared secondary VM instance and during execution of the individual service instance by the secondary VM instance:
• determining a difference between a resource level of the shared secondary VM instance and a target resource level associated with the corresponding individual service instance;
• and
• adjusting the current resource level of the secondary VM instance based on the difference.